The nucleus of a cell contains most of that cell's genetic material. Its job is to maintain the integrity of the cell while controlling its activities. The nucleus is separated from the cytoplasm by a membrane called a nuclear envelope.This helps to protect the cell's chromosomes which is where the DNA is located.

The nucleus was first discovered by microscopist Antonie van Leeuwenhoek in the mid-1600s while he was examining the red blood cells of salmon. The nucleus was again observed in 1804 by Franz Bauer and botanist Robert Brown, who described the nucleus in great detail in 1831.